1. Technical Field
The present invention relates to an image display apparatus.
2. Related Art
A head mounted display (HMD) has been known as a display apparatus that directly irradiates the retinae of a user's eyes with laser light to allow the user to visually recognize an image.
A head mounted display typically includes a light emitting apparatus that outputs light and a sweeper that changes the optical path of the outputted light in such a way that the user's retinae are scanned with the outputted light. The thus configured head mounted display allows the user to visually recognize, for example, both an outside scene and an image drawn with the sweeper at the same time.
For example, JP-A-2014-78022 discloses an image display apparatus including a light source, a sweeper that sweeps parallelized light emitted from the light source, and an optical apparatus that relays the parallelized light swept with the sweeper and outputs the relayed light toward a user's eyes. JP-A-2014-78022 further discloses that among the components of the image display apparatus, the optical apparatus includes a light guide plate configured to cause light incident thereon to propagate therethrough while undergoing total reflection and then exit out thereof, a first diffraction grating member that diffracts the light incident on the light guide plate in such a way that the incident light undergoes total reflection, and a second diffraction grating member that diffracts the light having propagated while undergoing total reflection in such a way that the light is allowed to exit out of the light guide plate.
The image display apparatus described in JP-A-2014-78022 is, however, so configured that the light swept with the sweeper is incident on the first diffraction grating member. Since the light incident on the first diffraction grating member is the light having been swept over a two-dimensional sweep range having a fixed area, the first diffraction grating member needs to be large enough to receive the light. As a result, the image display apparatus described in JP-A-2014-78022 inevitably has a large size.